[HN Gopher] DARPA wants to bypass the thermal middleman in nucle...
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DARPA wants to bypass the thermal middleman in nuclear power
systems
Author : bilsbie
Score : 53 points
Date : 2024-08-09 21:12 UTC (1 hours ago)
(HTM) web link (www.ans.org)
(TXT) w3m dump (www.ans.org)
| xhkkffbf wrote:
| If photovoltaic cells can create power from radiation in the
| visible light range, I suppose there might be radiovoltaics that
| can do something similar. But I wonder if they can capture the
| high power fluxes from a modern core.
| actionfromafar wrote:
| Mayne one could run it in the visible range, or almost there.
| Wasn't there some new kind of IR solar cells?
| ta988 wrote:
| You have to go the other way of the spectrum toward something
| that loves to avoid interacting with matter...
| exabrial wrote:
| Finally a use for dark matter
| baking wrote:
| I think the issue is the low absorption rate. Eli
| Yablonovitch proposed a box of PV cells facing inward
| containing a heat source where the IR light would bounce
| around until converted to electricity or absorbed as heat.
| This could be used inside a water heater so waste heat could
| be stored. Known as thermo-photovoltaics. See this talk I
| think: https://www.youtube.com/watch?v=lDxJsa8miNQ
| not2b wrote:
| Yes, I see how direct conversion could work with alpha and
| beta radiation, but it seems the gamma and the neutrons
| would just blast through everything and you'd capture only
| a tiny percent of the energy.
| baking wrote:
| Sorry, I was responding to the part about IR.
| geuis wrote:
| Helion https://www.helionenergy.com/technology/ is a commercial
| fusion company working on a design that theoretically would use
| direct energy capture from the magnetic fields generated during
| the fusion event. They made some headlines last year. Not clear
| if their approach will be successful but it certainly is an
| interesting approach.
| TheRealPomax wrote:
| Commercial _energy_ company. Not fusion company. There are no
| fusion companies on this planet yet.
| sigmoid10 wrote:
| Fusion is infinitely harder for this than fission. No company
| has demonstrated stable fusion with a positive net energy gain.
| Most of these startups are borderline scams for milking
| gullible VCs. Helion in particular has been around for more
| than a decade and was supposed to reach break even in 2023.
| They haven't even achieved a fully stable D-D reaction so far.
| The biggest thing it has achieved is siphoning tons of money
| from OpenAI's investors because of some questionable actions by
| Sam Altman.
| exabrial wrote:
| There definitely trendy since some high profile YouTubers were
| invited to tour! I sincerely hope they can succeed. I believe a
| limiting factor is going to be fuel unfortunately, as well as
| I'm not entirely sure it'll be radiation free.
| waryFormerNuke wrote:
| I don't remember the details, but the last time I looked into
| Helion I came away with the belief that their technology flat
| out doesn't make sense and will likely never be anywhere near
| net-positive. Like, the numbers literally don't add up and
| their design could never be anywhere near net-positive.
| Animats wrote:
| Nuclear batteries with beta emitters driving some kind of
| semiconductor have been around for a while, but they're very low
| power.[1]
|
| "... Betavolt's team of scientists developed a unique single-
| crystal diamond semiconductor that is only 10 microns thick,
| placing a 2-micron-thick nickel-63 sheet between two diamond
| semiconductor converters to convert the decay energy of the
| radioactive source into electric current to form an independent
| unit."
|
| "... 100 microwatts, a voltage of 3V, and a volume of 15 X 15 X 5
| cubic millimeters ..."
|
| 3-4 orders below the power requirements for a phone. An AirTag-
| type intermittent device, though...
|
| So, can those be scaled up? Are all those little beta-emitters in
| coin cell form factor going to be a problem? Nickel-63 has a half
| life of 100 years, so they'll be active for a while. Not
| dangerous unless broken up and ingested, but need to be kept out
| of the food chain.
|
| [1] https://www-betavolt-
| tech.translate.goog/359485-359485_64506...
| saulrh wrote:
| Not dangerous unless broken up and ingested, but need
| to be kept out of the food chain.
|
| No worse than a NiCad in that respect. Probably better, if
| anything, since it's so much easier to detect and track.
| giantg2 wrote:
| And set off all the NBC detectors on the highways near major
| cities.
| wizardforhire wrote:
| I always thought super conducting ccds with plasma scintillating
| cell intermediaries were the way to go.
|
| Capture the alpha and beta radiation with the plasma
| scintillators. Plasma being ideal because it wont degrade with
| bombardment.
|
| Capture the em radiation with ccds.
|
| We normally think of ccds as low power capture devices for
| cameras. Theres no reason they couldn't be scaled up to handle
| the power requirements. Perfect use case for super conductors.
|
| This of course for moderate to large scale fusion reactors where
| cost is a negligible object.
|
| Of course the dream is solid state Hau arrays. Which Dr Lene Hau
| postulated 15 years ago... but thats a whole other story.
| wizardforhire wrote:
| Of course plasma will degrade its just easier to separate out
| the products. You could feed the plasma back into the reactor
| and use cyclotron resonance. Alpha and Beta decay being one of
| the big problems with reactor design as the walls degrade over
| time. So designing for that with an active system seems to me
| to be a way a viable solution to minimize maintenance.
| epistasis wrote:
| This is pretty much the _only_ hope for nuclear power in the
| future. Current reactors are way too expensive, and they do not
| get cheaper the more we build of them.
|
| Miles upon miles of pipes with high-performance welds meant to
| last decades is no way to build a cheap and cost-effective
| electrical generation system. We need something better.
|
| Also, getting off a thermodynamic heat engine means the chance
| for far greater efficiency. Going through a heat cycle is hugely
| inefficient.
|
| For example, just extending the lifetime of the Diablo Canyon
| reactor pair in California, for five years extra life from 2025
| to 2030, is expected to cost a minimum of $8.3B. That's the
| utility's claim before the work has been done, and life all
| nuclear/construction projects, it will almost certainly balloon
| midway.
|
| TL;DR nuclear needs a tech breakthrough like direct conversion.
| at_a_remove wrote:
| This is one of the reasons why, as an undergrad, I switched from
| nuclear engineering to physics: at the end of the day, we're
| still using heat and turbines, just with extra, more dangerous
| steps; although the materials engineering aspect is recognizably
| challenging, I found it not particularly thrilling.
|
| At other, far end of the scale, if Hawking radiation does exist,
| black holes could be considered converters of mass to energy,
| skipping all of the conservation of baryon and lepton numbers ...
| although at very large timescales until you have a fizzy, spicy
| nano black hole on hand.
|
| Controlled capture of the various types of radiation (sometimes I
| find that word to be sloppy) to extract the kinetic energies does
| not seem to be physically impossible, but I have oft wondered
| _how_ as I think about various nuclear batteries which have
| existed. Indeed, the article doesn 't even break it down enough:
| beta ought to be split into beta-plus (positrons) and beta-minus
| (electrons), and they skipped some _2p_ emissions. My guess is
| that not only will each need its own approach, but that each of
| those would be subdivided into different energy bands, not unlike
| having different compounds for chlorophyll-A and chlorophyll-B,
| only for, say, fast neutrons versus thermal neutrons.
|
| And I think that's gonna be materials engineering again. Whoops!
| mannykannot wrote:
| In fission, it seems that most of the energy release is in the
| form of the kinetic energy of the daughter nuclei rather than
| gamma radiation or the kinetic energy of neutrons (from
| Wikipedia: _For uranium-235 (total mean fission energy 202.79
| MeV), typically ~169 MeV appears as the kinetic energy of the
| daughter nuclei, which fly apart at about 3% of the speed of
| light, due to Coulomb repulsion. Also, an average of 2.5 neutrons
| are emitted, with a mean kinetic energy per neutron of ~2 MeV
| (total of 4.8 MeV.) The fission reaction also releases ~7 MeV in
| prompt gamma ray photons._ )[1]
|
| Given this, I'm guessing that, for direct conversion to be at all
| efficient here, a significant fraction of this energy would have
| to be converted into electrical potential energy rather than be
| dissipated as heat in collisions between these nuclei and any
| part of the apparatus. Are there any nascent technologies of this
| sort?
|
| [1] https://en.wikipedia.org/wiki/Nuclear_fission
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